Geochemical maturity, litho-tectonic settings and source area paleoweathering characterization of the Cretaceous Mundeck and Mungo River Formation sandstones, North Western, Douala sub basin, West Africa: A petrographic and geochemical approach

Abstract

The Mundeck and Mungo River Formation sandstones located within the Douala sub basin in Cameroon were subjected to both petrographic and geochemical analyses to unveil their geological characterization such as chemical and mineralogical maturity, litho-tectonic setting, climate and weathering intensity of the source area at the time of their formation. Petrographic studies reveals that the sandstones show variable colours ranging from reddish to brownish, pinkish, grey and white with textures ranging from medium to coarse grained. The studied sandstones consist of various types of angular to sub angular, quartz, rock fragments, mica, feldspar. Modal analysis data and plots of detrital modes of the studied sandstones on Qt–F–RF diagrams suggest that they were derived from a plutonic source rock (igneous origin) with little or no contribution from metamorphic sources. Plot of the Qm–F–L diagram of the studied sandstones reveal a quartzose recycled and transitional continental provenance fields. Mineralogical classification of these sandstones from Qt–F–RF triangular diagram classifies them as arkose, lithic arkose and sub-litherarenite. Bivariate plot of Qp/(F + R) vs (Qm + Qp)/(F + R), SiO₂ Vs Al₂O₃ +K₂O + Na₂O coupled with values of Chemical index Alteration (CIA = 70–99) and plagioclase index Alteration (PIA>80) reveal a moderate to high intensity of weathering in the source area under a semi-humid to humid paleoclimatic conditions with high lixiviation of feldspars (PIA>80 %) for the studied sandstones. The mineralogical maturity index (MMI = 3–9) coupled with the new index of compositional variation (ICV_new <1) reveal that the sandstones are sub mature to mature. Geochemical binary plots of La/Sc, Th/Co, Th/Sc couple with plots of DF1vs DF2 and K₂O/Na₂O vs SiO₂ points to an igneous felsic source rock formed in a passive margin for the studied sandstones.